Surprising Behaviour of the Wageningen B-screw Series Polynomials

Undoubtedly the Wageningen B-screw Series is the most widely used systematic propeller series. It is very popular to preselect propeller dimensions during the preliminary design stage, but often it is also used to merely select the final propeller. Over time the originally measured data sets were faired and scaled to a uniform Reynolds number (based on chord length and section advance speed) of 2·10⁶ to increase the reliability of the series. With the advent of the computer polynomials for the thrust and torque values were calculated from the available data sets. The measured data are typically presented in the well-known open-water curves of thrust and torque coefficients K_T and K_Q versus the advance coefficient J. Changing the presentation from open-water diagrams to efficiency maps reveals some unsuspected and surprising behaviours, such as multiple optima when optimizing for efficiency or even no optimum at all for certain conditions. These artefacts get more pronounced at higher pitch to diameter ratios and low blade numbers. The present work builds upon the paper presented by the author at the AMT'17 and smp'19 conferences and now includes the extended efficiency maps, as suggested by Danckwardt, for all propellers of the Wageningen B-screw Series.